|Retrosaur Iguanodon, c. 1854. Based, of course, on the sublime work of Benjamin Waterhouse Hawkins.|
Undoubtedly, Iguanodon is a 'classic' dinosaur, and has been a mainstay of popular dinosaur literature for decades. Other dinosaur species named in the early 1800s have not enjoyed the same treatment (Thecodontosaurus, Ceitiosaurus and Hylaeosaurus for instance, are not household names), so its popularity is not just a result of it being one of the first dinosaurs known. Most of us can probably remember a key Iguanodon depiction from our childhood dinosaur books, magazines or films - or from a Love in the Time of Chasmosaurs vintage palaeoart post if you're not yet through puberty - with it stood upright and, of course, giving an irrepressible thumbs-up with its famous thumb spike. These Mesozoic Fonzies, which diehards always knew came in big (I. bernissartensis) and small (I. atherfieldensis) flavours, wouldn't stop manually approving their surroundings even when being attacked by passing generic 'megalosaurs'. Final revisions to its anatomy - an aloft tail and quadrupedal stance - have been drifting into popular depictions for years now, replacing MesoFonz with a heavyset herbivore often depicted living in herds and browsing at different levels. While its lack or truly bizarre anatomy or ferocity may have prevented Iguanodon from ever being the most famous of dinosaur species, there's little doubt that it's held a long-term place in palaeo-pop culture.
All good things...
At least, until recently. If the internet palaeo scene is anything to go by, Iguanodon seems to be sliding down the popularity pole at the moment. It just doesn't seem to be the topic of much conversation any more, or even artwork. Feathered theropods, weird sauropods, horned dinosaurs and even hadrosaurs - boring old hadrosaurs - seem to have stolen the limelight. Perhaps this is because our taxonomic and palaeobiological perceptions of many prehistoric animals have radically changed in recent years whereas Iguanodon, frankly, has remained rather static. It's a bit too familiar. Dinosaur palaeontology has changed radically in the last few decades, but it's changed around Iguanodon, which has done little more than tip forward a little since the 1980s. Discussions about feathers, postures, weird soft-tissue details and whatnot have passed it by entirely, and even a relatively recent shake-up of its taxonomy, where the Cretaceous-straddling, globe-spanning monster-Iguanodon genus was carved up into multiple genera spread across time and space (see Darren Naish's Scientific American articles here, here and here for details) did little to revive public interest in one of our longest serving and best-known dinosaurs. Iguanodon seems to be a dinosaurian washed-up Golden Age movie star: once great, now rarely mentioned, and only wheeled for nostalgia.
|The gossip magazines would have a field day.|
Iguanodonts: the undiscovered country
At the heart of this newfound complexity is the aforementioned reappraisal of iguanodont diversity. It's worth stressing that the charge to slay the waste basket monstergenus Iguanodon, started by Norman and Barrett (2002) and followed by the likes of Paul (2008), Norman (2010), Carpenter and Ishida (2010), Naish and Martill (2008), McDonald et al. (2010), McDonald (2012a, b) and others, was not a case of splitting minor taxonomic hairs. Unlike the differences which separate many fossil animals, most taxa pulled from Iguanodon are characterised by radically different morphology which would be obvious even in life. In Britain alone, the handful of species recognised as various members of Iguanodon may now comprise as many as nine genera (not counting objective synonyms). It's well known that Iguanodon is now monospecific, containing only the giant species I. bernissartensis. In the UK at least, this is principally known from the Wessex Sub-basin of the Wealden Supergroup of the Isle of Wight, although it also occurs in the Weald Sub-basin of Surrey, Sussex and Kent (below). It was joined in both basins by Mantellisaurus, the smaller iguanodont once called Iguanodon atherfieldensis and, in the Wessex, by two other possible taxa: Proplanicoxa galtoni and Dollodon bampingi. All but Proplanicoxa galtoni are known from elsewhere in Europe, which cannot be said for other British iguanodonts Barilium dawsoni*, Hypselospinus fittoni, Sellacoxa pauli and Kukufeldia tilgatensis from the Weald Sub-basin, also of the Wealden Supergroup of Sussex and Surrey. These animals are geologically older than the more familiar Iguanodon and Mantellisaurus and, for now at least, do not seem to overlap stratigraphically. A further genus, Owenodon hoggi, has been named for "Iguanodon" material from the British Purbeck Group. A number of other Asian and North American genera have also been pulled from Iguanodon, but the British record seems unusually diverse and implies that multiple iguanodonts existed in the same basins. Admittedly, exactly how many European iguanodont taxa are valid remains uncertain - there are arguments for it being over-split and overly-conservative - but even a relatively cautious assessment suggests several iguanodont faunas evolved in ancient Britain.
*Fascinating aside: according to Norman (2011a, b) there's a good chance that the original Iguanodon teeth belong to Barilium. There's not much we can do about this now - after years of confusion over what Iguanodon is, the name has been irreversibly transferred to I. bernissartensis. While most agree this was one appropriate cause of action to take - most of us have always thought of this species as the 'classic' Iguanodon - there are lots of niggles and issues with the choice of bernissartensis as the surrogate type species of Iguanodon. The similarity of the original 'I. anglicus' teeth to Barilium is just another hangover from the excessive lumping that Iguanodon experienced in its first 180 years of recognition.
long proved controversial, but a role in stabbing generic theropods in the neck is a common assumption. This long-held assumption is questioned by the range of morphologies associated with the pollex however. Most of us are familiar with the general construction of the iguanodont pollex thanks to oft-reproduced images of the Iguanodon hand, such as...
|Left Iguanodon bernissartensis manus. Image from here.|
The bit where I stop writing
In sum, while it would be silly to say that iguanodont science is undergoing anything like a revolution or renaissance, there's certainly a lot of tinkering going on and the results are exciting whatever your specific taste in palaeontology - taxonomic, functional, or palaeoecological. Granted, the outcome of these ongoing studies are not going to make newspaper headlines, but if you're interested in dinosaur palaeobiology - and you are if you've read this far - then this should be very cool, interesting stuff. If the apparent decline in public interest for iguanodonts is because many of us consider them overly-familiar, then we need to think about changing that attitude. Far from being 'done to death', after many decades of fairly static interpretation, iguanodont science is becoming more interesting than ever.
For an easy to access, relatively up to date and inexpensive look at a bunch of iguanodonts, you could do a lot worse than checking out Dave Norman's chapter on ornithopods in English Wealden Fossils (Norman, 2011b). Further brief musings on the decline of a dinosaur celebrity are provided in this post on Stegosaurus.
- Carpenter, K., & Ishida, Y. (2010). Early and “Middle” Cretaceous iguanodonts in time and space. Journal of Iberian Geology, 36(2), 145-164.
- Paul, G. S. (2008). A revised taxonomy of the iguanodont dinosaur genera and species. Cretaceous Research, 29(2), 192-216.
- McDonald, A. T. (2012a). Phylogeny of basal iguanodonts (Dinosauria: Ornithischia): an update. PloS one, 7(5), e36745.
- McDonald, A. T. (2012b). The status of Dollodon and other basal iguanodonts (Dinosauria: Ornithischia) from the Lower Cretaceous of Europe. Cretaceous Research, 33(1), 1-6.
- McDonald, A. T., Barrett, P. M., & Chapman, S. D. (2010). A new basal iguanodont (Dinosauria: Ornithischia) from the Wealden (Lower Cretaceous) of England. Zootaxa, 2569, 1-43.
- Naish, D., & Martill, D. M. (2008). Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, 165(3), 613-623.
- Naish, D., & Sweetman, S. C. (2011). A tiny maniraptoran dinosaur in the Lower Cretaceous Hastings Group: evidence from a new vertebrate-bearing locality in south-east England. Cretaceous Research, 32(4), 464-471.
- Norman, D. B. (2010). A taxonomy of iguanodontians (Dinosauria: Ornithopoda) from the lower Wealden Group (Cretaceous: Valanginian) of southern England. Zootaxa, (2489), 47-66.
- Norman, D. B. (2011a). On the osteology of the lower Wealden (Valanginian) ornithopod Barilium dawsoni (Iguanodontia: Styracosterna). Special Papers in Palaeontology, 86, 165-194.
- Norman, D. B. (2011b). Ornithopod dinosaurs. In: Batten, D. J. (ed.) English Wealden fossils. The Palaeontological Association (London), pp. 407-475.
- Norman, D. B., & Barrett, P. M. (2002). Ornithischian dinosaurs from the lower Cretaceous (Berriasian) of England. Special Papers in Palaeontology, 68, 161-190.